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  <div class="section" id="checkcxxcompilerflag">
<span id="module:CheckCXXCompilerFlag"></span><h1>CheckCXXCompilerFlag<a class="headerlink" href="#checkcxxcompilerflag" title="Permalink to this headline">¶</a></h1>
<p>Check whether the CXX compiler supports a given flag.</p>
<dl class="command">
<dt id="command:check_cxx_compiler_flag">
<code class="sig-name descname">check_cxx_compiler_flag</code><a class="headerlink" href="#command:check_cxx_compiler_flag" title="Permalink to this definition">¶</a></dt>
<dd><div class="highlight-cmake notranslate"><div class="highlight"><pre><span></span><span class="nf">check_cxx_compiler_flag(</span><span class="nv">&lt;flag&gt;</span><span class="w"> </span><span class="nv">&lt;var&gt;</span><span class="nf">)</span><span class="w"></span>
</pre></div>
</div>
<p>Check that the <code class="docutils literal notranslate"><span class="pre">&lt;flag&gt;</span></code> is accepted by the compiler without
a diagnostic.  Stores the result in an internal cache entry
named <code class="docutils literal notranslate"><span class="pre">&lt;var&gt;</span></code>.</p>
</dd></dl>

<p>This command temporarily sets the <code class="docutils literal notranslate"><span class="pre">CMAKE_REQUIRED_DEFINITIONS</span></code> variable
and calls the <code class="docutils literal notranslate"><span class="pre">check_cxx_source_compiles</span></code> macro from the
<span class="target" id="index-0-module:CheckCXXSourceCompiles"></span><a class="reference internal" href="CheckCXXSourceCompiles.html#module:CheckCXXSourceCompiles" title="CheckCXXSourceCompiles"><code class="xref cmake cmake-module docutils literal notranslate"><span class="pre">CheckCXXSourceCompiles</span></code></a> module.  See documentation of that
module for a listing of variables that can otherwise modify the build.</p>
<p>A positive result from this check indicates only that the compiler did not
issue a diagnostic message when given the flag.  Whether the flag has any
effect or even a specific one is beyond the scope of this module.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Since the <span class="target" id="index-0-command:try_compile"></span><a class="reference internal" href="../command/try_compile.html#command:try_compile" title="try_compile"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">try_compile()</span></code></a> command forwards flags from variables
like <span class="target" id="index-0-variable:CMAKE_&lt;LANG&gt;_FLAGS"></span><a class="reference internal" href="../variable/CMAKE_LANG_FLAGS.html#variable:CMAKE_&lt;LANG&gt;_FLAGS" title="CMAKE_&lt;LANG&gt;_FLAGS"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_CXX_FLAGS</span></code></a>, unknown flags
in such variables may cause a false negative for this check.</p>
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